In recent years, injury of personnel by bomb called IED (Improvised Explosive Device) is increasing in conflict areas. IED is difficult to find, because there are many different type of IED and the explosion power is not constant. Therefore, MRAP (Mine Resistant Ambush Protected) Vehicle and BMS (Blast Mitigation Seats) are being developed in some countries. In this paper, we develop the system of the seat to reduce the acceleration from the explosion-shock for BMS. We developed new electromagnetic support system. The response of new system is more quick than the conventional mechanism and the response threshold is adjustable. The effect of the electromagnetic support system was confirmed by experiment.